"We had the suspect upstairs. The homicide unit talked to him. Right away he didn't have anything to say, but then he stated he pledges his allegiance to Islamic State, he follows Allah and that's the reason he was called upon to do this," authorities said in a press conference.

Police say Archer ran up to Hartnett's police car and fired 13 shots, hitting the officer three times in an arm. Hartnett was able to get out of his car, chasing Archer and shooting him three times. (Video via KSAZ)

Archer's pledge to ISIS is sure to inflame already-high fears of lone-wolf terrorism. A Gallup poll taken in the wake of attacks in Paris and San Bernardino found Americans name terrorism as the country's No. 1 problem.